The invention relates to a form-fill-seal device for forming bags from a web-shaped foil material, filling them with products and subsequently sealing them, the foil web prior to being transformed on a form shoulder into a foil tube being provided with zipper strips for providing the bags to be made with a zipper sealing.
It is known with continuously running form-fill-seal machines, wherein the foil web is continuously drivenxe2x80x94at a uniform speed or otherwisexe2x80x94by driving belts positioned at the location of the filling station, to apply the zipper strips at the foil web by means of a zipper strip application station placed on a carriage, which during the application of the zipper strip is moved along with the moving foil web. A drawback of this is that the movement of the heavy carriage generates forces due to which the course of the machine becomes unsteady and failures occur more easily. Moreover the moveable carriage seriously limits the operating speed of the machine.
In another device some improvement on this is offered in that downstream of the zipper strip application station a moveable turn roller has been provided, with which during the continuous passage of the foil web a buffer length can be formed, which during the application of the zipper strip (when the foil web in the track of the supply roll up to the turn roller is kept still) can be discharged in order for the operation of the form-fill-seal means downstream of the turn roller not having to be interrupted. During application of the zipper strip the supply roll for the foil web is kept still.
A drawback of this is that time and again the supply roll has to be put to a standstill and into motion again, as a result of which considerable forces are exerted on the foil web, which as a result has varying web tensions resulting in an inaccurate course of the foil web in the machine and possibly failures. Furthermore the drive of the foil web has to be adapted for forming the correct buffer length in between the moments of activation of the zipper strip application station.
It is an object of the invention to improve on this.
From one aspect the invention to that end provides a form-fill-seal device for forming bags from a web-shaped foil material, filling them with products and subsequently sealing them, the device comprising a foil supply station having means for holding a roll of foil web, a form shoulder for transforming the foil web into a foil tube and a station placed between the supply station and the form shoulder for applying a zipper strip transverse to the foil web for each bag to be made, the foil web following a first transport track between the supply station and the application station and a second transport track between the application station and the form shoulder, respectively, the device comprising means for continuously driving the foil web, the device further comprising means for forming a buffer length of foil web, which buffer means comprise first foil web diversion means and second foil web diversion means, which engage onto the first and second track of the foil web, respectively, and are connected to each other for simultaneous but opposite movement by buffer drive means towards the first track and away from the second track, respectively, and vice versa, while taking up and discharging, respectively, equal lengths of foil web.
Thus a buffer length can be formed and discharged on both sides of the application station, in such a relation that in the period between the arranging of two zipper strips, a buffer length of foil web is formed downstream of the application station which is equal to a buffer length formed upstream of the application station during the application of a zipper strip. As a result the foil web is able to keep on running at constant speed both downstream and upstream of the buffer device, while during the application of the zipper strip the foil web can be kept still at that location.
In a simple embodiment the first and second foil web diversion means have been adapted for performing opposite movements of equal length.
The first and second foil web diversion means have preferably been arranged on respective arms of a lever, the buffer drive means engaging on the lever for reciprocally tilting it about a tilting shaft. With such a lever, both lever arms being of equal length, buffer formation and discharge can take place in a failure-proof manner.
Preferably the lever has been fixedly arranged on the tilting shaft and the tilting shaft is driven preferably by a servo motor. The driving can thus take place directly an accurately, in which the movement cycle can be adjusted for a smooth motion of the lever.
The accuracy of the process is further increased when a foil web brake has been arranged between the first foil web diversion means and the application station for keeping the foil web still between the first and the second foil web diversion means during the operation of the application station.